The present invention relates to a hot chamber die-casting machine with a gooseneck located in a metal bath within a smelter, with a vertical channel between the bottom of the sleeve and the seat of nozzle body with a mouthpiece and a nozzle mounted thereon as well as two drive assemblies having axes which are parallel to the nozzle. The assemblies are connected with a crossarm of a machine stand associated with the smelter and with a solid molding plate of a closing unit to which half of a mold is fastened, whose feed bush can be pressed against the nozzle tip during a casting process.
Known hot chamber die-casting machines which are on the market, like those manufactured and sold by the applicant, for example (Frech die-casting automatic machine DAW 80S xe2x80x9cDruckvermerkxe2x80x9d 06.94 KK), have a hydraulic drive in the form of two mutually parallel hydraulic cylinders, each engaging the mold on the solid mold plate, in order to advance the feed bush and press it against a nozzle tip. The cylinders are connected, on a side facing away from the mold plate, with a crossarm of the machine stand that spans the furnace and the crucible. This design is provided in order to permit moving and applying the feed bush to the mold at the nozzle tip with a given feed rate through the hydraulic system. The very high application force required during die casting can also be maintained by such drives. A certain disadvantage of this is that the hydraulic cylinders that usually run horizontally above the furnace grow hot; their regulating ability is also influenced by the variable viscosity of the hydraulic oil used, and this is taken into account.
It is also already known (AT-PS 292 222) to provide an electrical drive for a threaded spindle arrangement for closing a mold of an injection molding machine. Since molds of injection molding machines, and also molds of hot chamber injection molding machines, are not located in immediate vicinities of crucibles or furnaces which receive the hot metal melt, there are fewer problems with using electric motors than there are with advancing and retracting drives for feed bushes in hot chamber die-casting machines, in which these drives must necessarily be located directly in the areas of the hot melt.
One goal of the invention is to design a drive assembly for advancing a mold to a nozzle in such a fashion that feed regulation that is as time-optimized and precise as possible, and which is independent of temperatures developing in such die-casting machines, can be achieved.
To achieve this goal, in a hot chamber die-casting machine of the type mentioned above, the drive assembly is designed as a linear drive driven by electric servomotors with feed rates which can be controlled. This design makes a very delicate adjustment of the feed bush to the nozzle to the mold with varying speeds possible without any influence from the changing viscosities of hydraulic oil. A high adjustment rate combined with a delicate adjustment largely correspond to an optimum process so that a considerable improvement over known hydraulic systems is achieved.
Especially advantageously, the influence of heat from the crucible and the furnace is avoided by having the rotational axes of the servomotors located above the crucible and the oven connected to the linear drive through an angle drive and aligned approximately vertically. By this measure, the servomotors are located as far as possible from the furnace and brought into a position in which the heat flow from the oven or crucible is as small as possible. The angle drive located closer to the furnace provides a certain amount of heat insulation and can additionally be provided with a layer of insulation. The linear drive can be designed as a spindle drive and may additionally be surrounded by a continuous cooling jacket as well. It is also possible to equip the servomotors with water cooling. A rack and pinion drive can also form the linear drive, although a spindle drive has proven advantageous.
To obtain good travel of the spindle drive, a roll spindle or ball screw arrangement, which itself is known, can also be provided and may have a pitch which is made so that it has a self-locking effect. Consequently, unintentional feed or retraction of the drive is prevented, and the necessary retaining pressure can also be maintained during the die-casting process. Of course, corresponding locking devices can also be provided. In addition, the engine load moments are controlled so that a reliable closure between the feed bush and the nozzle tip is ensured.
According to one feature of the invention, the servomotors can be operated at different rates, with the arrangement being made such that the feed rate of the drive shortly before the application of the nozzle tip is reduced considerably relative to the feed rate. In this manner, it is possible to bring the feed neck against the nozzle tip in a precisely regulated fashion. As a result, wear at this point can be largely avoided. It is known to harden the nozzle tip, and the nozzle tip abuts the feed bush over a very small contact area. If the impact is too hard, damage can occur to the nozzle tip; this damage is avoided by the design of the invention.
An embodiment of the invention is shown in the drawings and is explained below.